Assume there is no prospective investment project that will yield an expected rate of return after interest of 25 percent or more, but that there are $5 billion of investment opportunities that will yield expected rates of return after interest rates between 20 and 25 percent, and additional $5 billion for expected rates of return after interest between 15 and 20 percent, etc. If the real interest rate in the economy is 15 percent, the aggregate amount of gross investment will be:

A. $10 billion

B. $25 billion

C. $15 billion

D. $20 billion